In order to function, the human brain relies on neurotransmitters binding to certain receptors, which in turn initiate a biological response in us, such as a muscle movement or an emotion. Some details of this process are well described and others are not. It is not clearly known how certain receptor types may influence the behaviors we see, but general patterns are understood.
When drugs enter the brain, they bind to receptors and trick us into feeling a response- and that response is the 'high'. If drugs were not able to cause these good feelings, they wouldn’t be abused.
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The problems arise in two ways. The first way is tolerance. Tolerance is the body’s reaction to repeated doses of a drug. Just like skin reacts to form a callus when an area is used over and over again, the receptors in the brain change to meet the new condition of having a drug around. With tolerance, more is needed to get a similar effect from the drug.
Drugs that mimic natural neurotransmitters begin to replace those normally present in the brain. The body senses the ‘fakes’ as real and quits making normal levels. When patients stop the drug, suddenly the body is caught short and cannot immediately meet what it senses as a lack of neurotransmitter. This is one of the reasons withdrawal happens.
The second phenomenon is dependence. Partly, this is a physical need for the drug because of the changes mentioned above. But there is a psychological need that develops as well. Often, drugs are used to self-treat depression or to avoid problems. As the addict becomes dependent on the drug, behavioral changes occur that go beyond simple brain chemistry.
Even after withdrawal has been completed, addicts may still have cravings for it. This cannot be explained on the basis of neurotransmitters alone, because the normal biochemistry has been restored. Current understandings are that whole areas of the brain that are tied to pleasure and reward have been altered and may remain so for years, if not a lifetime.
Perhaps a genetic predisposition to this profound and long lasting type of addiction may be one answer. Much remains to be studied. For now, addictions are treated as chronic diseases and it is felt there is always some risk for relapse, even after years of abstinence.
photo by Artem Chernyshevych